The present invention relates to a fire resistant optical cable. More particularly, the present invention relates to a fire resistant optical cable which is able to resist to fire and to maintain its optical transmissive properties during and after the fire occurrence for a predetermined period of time.
Optical cables are generally used for medium or long distance telecommunications. There are specific applications where optical cables must have some ability to withstand fire aggression without significantly decreasing their transmission performance. For instance, cables used in fire alarm systems and/or local video surveillance must be able to continue to transmit data/signals in the presence of fire. The functionality of the optical cable must be maintained during the fire occurrence and usually also for a predetermined period of time after the fire is extinguished. Such kind of optical cables are usually installed in galleries and in buildings.
U.S. Pat. No. 5,173,960 discloses a fire retardant communication cable including a core which comprises at least one transmission media and fire retardant means which includes a material comprising a mixture of a first inorganic oxide constituent and a second inorganic oxide constituent. The first inorganic oxide constituent is characterized by melting when exposed to temperatures as low as about 350° C., whereas the second inorganic oxide constituent begins to crystallize at about 650° C. The fire retardant means is effective when said cable is exposed to temperatures in the range of about 350° C., to 1000° C., to form a crusty layer which insulates said core from heat energy and minimizes release of smoke and combustible gases. The fire-retardant means may be included as a jacket of the cable or as a longitudinally extending tape. Preferably, the fire retardant means is coextruded with the jacket. The transmission media may include one or more pairs of insulated metallic conductors or optical fibers.
International patent application WO 2010/012932 relates to a power and/or telecommunication cable comprising at least one conductive element surrounded by at least one insulating layer extending along the cable, the insulating layer being obtained from a composition containing the following compounds: a) an organic polymer, b) an inorganic compound containing a potassium oxide and/or one of the precursors thereof; c) a boron oxide and/or one of the precursors thereof; and d) calcium oxide CaO and/or one of the precursors thereof. The amount of the compound d) is at least 10 wt % of the total weight of the compounds b, c, and d in the composition. The above combination of inorganic fillers is able to react upon exposure to fire to produce a ceramic refractory material, which allows to maintain mechanical and electrical integrity of the cable during tire.